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The genes encoding a protein antigenic during the acute phase (SAPA) and another one antigenic during the chronic phase (antigen 30) of human Chagas' disease were analyzed in 15 Trypanosoma cruzi isolates and clones collected in distant geographical regions. These two genes had tandem repeats which were present in all parasites tested. However, large differences in the length of restriction fragments were observed among isolates. This was readily explained by variations in the number of repeat units present in homologous genes. This result was confirmed after analysis of 3 members of the SAPA gene family. In the case of antigen 30, we propose that differences in the number of repeat units result in size differences in the corresponding RNAs and proteins, which explains the large size heterogeneity in otherwise homologous T. cruzi antigens.

The cluster of alternated alpha- and beta-tubulin genes in the genome of Trypanosoma cruzi was shown to be transcribed into a single RNA molecule which upon processing gives rise to the mature alpha- and beta-tubulin mRNAs. This conclusion was based on: (i) nuclear RNA species with the same molecular mass hybridize to both alpha- and beta-tubulin cDNA probes; (ii) S1 nuclease assay of the clustered tubulin genes has shown protected DNA fragments of the same size and of greater molecular mass than that corresponding to the mRNAs, hybridizable to both alpha- and beta-tubulin cDNA probes; (iii) beta-tubulin hybrid selected RNA is still able to hybridize to alpha-tubulin probe.